1. Field of the Invention
The invention relates to communication systems, and in particular to activation of services in communication systems that facilitate packet data communication sessions.
2. Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities such as user equipment and/or other nodes associated with the communication system. The communication may comprise, for example, communication of voice, data, multimedia and so on. A session may, for example, be a telephone call type session between users or multi-way conference session, or a communication session between a user equipment and an application server (AS), such as a service provider server.
A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely, user equipment is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters which shall be used for the connection may also be defined. In other words, a specific set of “rules” on which the communication can be based on needs to be defined to enable communication by means of the system.
Communication systems providing wireless communication for user equipment are known. An example of the wireless systems is the public land mobile network (PLMN). The PLMNs are commonly based on cellular technology. In cellular systems, a base transceiver station (BTS) or similar access entity serves mobile user equipment (UE) via a wireless interface between these entities. The communication on the wireless interface between the user equipment and the elements of the communication network can be based on an appropriate communication protocol. The operation of the base station apparatus and other apparatus required for the communication can be controlled by one or several control entities. The various control entities may be interconnected.
One or more gateway nodes may also be provided for connecting the cellular access network to other networks e.g. to a public switched telephone network (PSTN) and/or other communication networks such as an IP (Internet Protocol) and/or other packet switched data networks. In such arrangement the mobile communications network provides an access network enabling a user with a wireless user equipment to access external networks, hosts, or services offered by specific service providers. The access point or gateway node of the mobile communication network then provides further access to an external network or an external host. For example, if the requested service is provided by a service provider located in other network, the service request is routed via the gateway to the service provider. The routing may be based on definitions in the mobile subscriber data stored by a mobile network operator.
An example of the type of services that may be offered for user such as the subscribers to a communication systems is the so called multimedia services. Some of the communication systems enabled to offer multimedia services are known as Internet Protocol (IP) Multimedia networks. IP Multimedia (IM) functionalities can be provided by means of an IP Multimedia Core Network (CN) subsystem, or briefly IP Multimedia subsystem (IMS). The IMS includes various network entities for the provision of the multimedia services. The IMS services are intended to offer, among other services, IP based packet data communication sessions between mobile user equipment.
In an packet data network a packet data carrier may be established to carry traffic flows over the network. An example of such a packet data carrier is a packet data protocol (PDP) context. A PDP context may be provided for various purposes, for example for transportation of signalling data and for transportation of payload data, i.e. for the control plane and for the user plane data communication. A data communication session between a user equipment and another party may be carried at least on the access network of the user equipment on a PDP context.
It is expected that various types of services are to be provided by means of different Application Servers (AS) over Internet Protocol Multimedia subsystem (IMS). Some of these services may be time critical. An example of the time-critical services that may be provided over the IMS are the so called direct voice communication services. A more specific example of these is the “Push-to-talk over Cellular” (PoC) service, also known as PTT, Push-To-Talk service. The direct voice communication services are intended to use the capabilities of the IP Multimedia Subsystem (IMS) for enabling IP connections for mobile user equipment and other parties of the communications, for example other mobile user equipment or entities associated with the network. The service allows the users to engage in immediate communication with one or more other users.
In PoC services communication between a user equipment and a PoC application server commonly occurs on a one-way data communications media. A user may open the data communications media by simply pushing a tangent key, for example a button on the keyboard of a user equipment or by otherwise activating the communications media. The activation means may be a specific button or tangent or any appropriate key of the keyboard. While a user speaks, the other user or users may listen. Bi-directional communication can be offered since all parties of the communications session may similarly communicate voice data with the PoC application server. The turns to speak are requested by activating the communication media, e.g. by pressing the push-to-talk button. The turns may be granted for example on a first come first served basis or based on priorities. Users can join the group session they wish to talk to and then activate the media to start talking.
In service application such as PoC one-to-one call the calling party may need to know when a ‘floor’ is granted for the calling party in the beginning of the call. The term ‘floor’ refers to data communication media resources that may be used for the communication of voice data.
A floor may be seen as a permission to temporarily access, manipulate or otherwise use a specific shared resource or a set of resources. A “floor” can be granted even when no data communication channel is yet available.
If no floor is granted, the calling party may not be able to start sending voice data to the PoC application server. Similarly the called party must know that the floor has been taken by the calling party. This must somehow be indicated to the parties during the call setup sequence.
In the prior art described, for example, by PoC Industry Consortium Specifications, the indication of a granted floor is sent through a specific floor control protocol, typically by means of a Real-time Transport protocol Control Protocol (RTCP). This approach requires creation and sending of separate messages for the floor status indications. In this approach a calling party of a PoC session has to send first an SIP INVITE message containing a Session Description Protocol (SDP) offer. After receiving this the PoC application server has to communicate in a separate message to the calling party an Real-time Transport protocol Control Protocol (RTCP) indication that a floor has been granted for use in the session.
Because PoC services do not commonly use preconditions there is no guarantee that media bearers are ready when a PoC application server sends one or more floor control messages. This may cause a problem, for example, when a user equipment is using a dedicated signalling PDP context, since the dedicated signalling PDP context does not allow transportation of RTCP traffic. For example, it is possible that no data carrier may have yet been activated for the data communication media at this point since the SDP answer has not yet been received. Thus the RTCP packet may need to be carried within some pre-existing data carrier, for example a pre-existing PDP context. However, if a user equipment is using a dedicated signalling PDP context, it is not allowed to transport Real-time Transport Protocol (RTP) nor Real-time Transport protocol Control Protocol (RTCP) packets within the PDP context. In this case the gateway between the access network and the data network will simply drop all incoming packets which do not comply with a acceptance policy of gateway and therefore a user equipment may not get any floor control messages prior secondary PDP context activation. It is only after receiving the final response carrying SDP answer to the initial INVITE message that the calling party can actually start sending media packets. Similarly on the called party side the PoC application server first sends an INVITE with an SDP offer. After receiving the final answer which carries an SDP answer, the PoC application server can send the called party an RTCP indication that the floor has been taken.